Fatty acids are carboxylic acids having varying degrees of unsaturation and molecular weight. Fatty acids are used in a wide variety of products, such as in soaps and surfactants, lubricants, paints and coatings, candles, and in a variety of other agricultural, industrial, and personal care products. Glycerine, or 1,2,3-propanetriol, is used as a humectant, plasticizer, emollient, and lubricant in a wide variety of industrial and personal care applications.
Though fatty acids and glycerine have been produced synthetically, a substantial portion of these materials are obtained from naturally derived fats and oils. Fats and oils are also known as triglycerides, which are the reaction products of an alcohol, glycerine, and an acid, the fatty acids discussed above. To produce fatty acids and glycerine from fats and oils, the fat or oil is hydrolyzed or "split", typically by the action of heat and pressure in the presence of water, to break the bonds between the acid and the alcohol.
Typically, the fat or oil is split commercially in a pressure splitter wherein preferably the fat or oil is introduced at one end and water introduced at the opposite end thereof in a countercurrent flow pattern. In operation, the pressure splitter provides substantial amounts of heat and pressure to the mixture of triglyceride and water to effect the hydrolysis. However, because the triglyceride is hydrophobic, the amount of actual contact between the water phase and the fat phase is relatively low. It is believed that after a period of time in the splitter individual triglyceride molecules incompletely hydrolyze, splitting off one acid molecule to create a di-glyceride or two acid molecules to form a monoglyceride. The mono- and di-glycerides are less hydrophobic than the starting triglyceride, and mix more thoroughly with water. As a result, the mono- and di-glycerides function as emulsifiers to improve mixing of the triglyceride with water. Under the turbulent conditions within the pressure splitter, it is believed that the mono- and di-glycerides improve the extent of mixing between the triglyceride and water, thereby facilitating the hydrolysis reaction.
The period of time during which the hydrolysis rate is depressed is known as the induction period. During the induction period, heat is inputted to the pressure splitter and pressure is generated, but few hydrolysis products are being produced. The volume of triglycerides hydrolyzed within the pressure splitter would be increased substantially if the induction period could be eliminated or at least substantially reduced.
Several methods have been used in the past to decrease the induction time in the pressure splitter. Surfactants have been added to the triglyceride feed to aid mixing between the water and fat layers in what became known as the Twitchell process. These surfactants were typically organo-sulphonic acids. However, after the splitting operation the surfactants had to be removed from the system, typically by extraction, which was time consuming and difficult to accomplish. Also, catalysts have been used to increase the rate of hydrolysis of the triglyceride and thereby the amount of mono- and di-glycerides. However, after the splitting operation was completed, the catalysts had to be removed from the system to eliminate undesirable contamination effects. It was also known that starting the pressure splitting operation with a fat or oil having a relatively high acid value would result in a decreased induction period in the splitting process. This could be accomplished by back-adding a blend of free acids, mono- and di-glycerides to the fat or oil feedstock. However, this step would not increase the overall efficiency of the pressure splitting process because a portion of the raw feedstock had to be replaced with the partially hydrolyzed portion. In effect, a portion of the feedstock had to be recycled through the splitter instead of subjecting the feedstock to splitting only once. In yet another method for decreasing the induction period, the feedstock in a storage tank prior to pressure splitting could be subjected to high temperatures in the presence of water to force the hydrolysis reaction to begin. However, the subjection of the feedstock to such high temperatures, in a range above about 80.degree. C., would cause formation of undesirable oxidation products and color bodies which would degrade the quality of the feedstock.